CA1080240A - Preparation of esters of thiocarbamic acids - Google Patents

Abstract

Abstract of the Disclosure Esters of thiocarbamic acids are prepared by a process comprising reacting COS with an amine of the formula at a COS/amine mole ration of at least about 0.502, and reacting the product of the above with an organic halide of the formula R3X
at a temperature of at least about 50°C, both reactions occurring in an anhydrous medium.
The symbols R1,R2, and R3 independently represent alkyl, alkenyl, alkynyl, aryl, aralkyl, cycloalkyl, cycloalkenyl, alkoxy, alkenyl, alkylthioalkenyl, or heterocyclic ring groups, optionally substituted.

Description

~080Z40 Cross Reference of Related Applications This patent application i3 a continuation-in-part of Application Serial No. 729,569, filed October 4, 1976.

Background of the Invention The esters of thiocarbamic acids are useful for a variety of purposes. Some are active herbicides, others are effective for inhibiting the growth of micro-organisms such as bacteria, and still others are active insecticides. The following is a group of processes representative of those known in the art for the preparation of these compounds.

The process of U.S. Patent 2,983,747 employs zinc chloride as a catalyst in the direct reaction of csrbamyl chlorides with mercaptans to produce various thiocarbamic esters.
Although the reaction can be conducted without the use of a solvent, a solvent inert to the catalyst, such as an organic solvent, must be used if a solvent is employed.

U.S. Patent 2,913~327 teaches a process involving the preparation of the sodium salt of a mercaptan followed by reaction with a carbamyl chloride in the presence of a solvent. The use of the sodium salt of the mercaptan causes problems of filtration and solids handling. The use of a solvent reduces reactor capacity throughout and can create a recovery problem. Furthermore, the hydrogen evolved during the preparation of the sodium salt causes a disposal problem.

U.S. Patent 3,836,524 describe~ a process involving the reaction of a carbamyl chloride with a mercaptan in the presence ~..

-2~

~0 8~ ~ 40 of an aqueou~ solution of a caustic agent. This process requires considerable agitation in order to form a high interfacial area between the two liquid phases, as well as a high caustic concen-tration in order to achieve the desired conversion and product purity.

U.S. Patent 3,133,947 describes a process which comprises reacting a secondary or primary am~ne with carbonyl sulfide in the presence of a basic material which may be any amine, including a tertiary amine, and thereafter reacting the intermediate with an organic sulfate, such as a dialkyl sulfate, or a diallyl sulfate.
Alkyl sulfate values are lost in this process, thus adding to the overall expense.

Carbonyl sulfide is reacted with a pr i ry or secondary amine in aqueous alkaline solution at temperatures of 20C or below in the process taught by U.S. Patent 3,167,571. Condensation of the amine salt of the thiocarbamic acid is then effected by reaction of the salt with an organic halide. There are two dis-advan~ages to this process. First, lo~er ac~ivity organic halides will not react at this temperature. Although such less active halides will readily react at temperatures around 100C, such temperatures cannot be used in this process since ~he aqueous medium will not absorb the COS at temperatures much in excess of 20C.
Second, close control is required of the amount of COS used since excess amounts cause decomposition of the thiocarbama~e. Thus, by-products are obtained in significant amounts, controllable only with a sacrifice in yield.

1~3VZ40 Low temperatures are also required in the process taught by U S Patent 3,151,119, wherein disadvantages similar to the above are encountered.

The most recent proces~ involving the use of COS is found in U.S. Patent 3,954,729, where a secondary amine i9 reacted with carbonyl sulfide in the presence of an aromatic solvent to form an amine salt of a thiocarbamic acid, which is then reacted with an alkyl halide to form the thiocarbamic acid ester. At stoichiometric mole ratio3 of carbonyl suliide to amine, however, a maximum 92% purity of the product was reported with no product aging. Aging and carbonyl sulfide excesses both lowered the purity even further. Thus, in order to hold the product purity up, this patent teaches that it is necessary to use at least a 4% molar deficit of carbonyl sulfide in the first reaction, and a very closely stiochiometric amount of the alkyl halide in the second reaction.
To achieve both maximum production per batch and minimum amounts of by-products, a high degree of accuracy is required in measuring relative reactant quantities. This is undesirable because of the expense of the extra monitoring and lack of flexibility. By-product formation is further held down by restricting the reaction tempera-ture in the second reaction to between 0 and 60C. Although the alkyl halides disclosed in the examples of the patent will react at a reasonable rate in this temperature range, the same is not true of the less active alkyl halides. For example, the lower alkyl chlorides will react extremely sLowly or not at all within this temperature range.

In view of these problems9 it is the object of this invention to provide a process for the preparation of thiocarbamic acid esters which provides high yields and conversions as well as a savings in starting materials and operating expenses.

It is a further object of this invention to provide a process for the preparation of thiocarbamic acid esters which does not require the precise monitoring required in the process of U.S.
Patent 3,954,729, and which will permit utilization of the alkyl chlorides which are unreactive in the latter process.

Summary of the Invention This invention relates to a novel method of preparing members of the class of compounds known as thiocarbamates, or thiocarbamic acid esters. The synonym thiolcarbamate ~s also used in the art to designate the same class of compounds. The term "thiocarbamic acid ester" will be used herein.

It has been discovered that, with the use of the novel process, thiocarbamic acid esters in high yield and purity can be prepared in an efficient and economical process. In particular, this invention relates to a method of preparing a thiocarbamic acid ester by a process which comprises (a) reacting COS with an amine of the formula Rl R2_NH
in which Rl and R2 are independently selected from the group consisting of hydrogen and the following substituted or unsubs~ituted groups: alkylg alkenyl, alkynyl, 10 8~ 2 40 aryl, aralkyl, cycloalkyl, cycloalkenyl, alkoxy, alkenoxy, alkoxyalkyl, alkylthioalkyl, alkoxyalkenyl, alkylthioalkenyl, and heterocyclic ring groups;
wherein the substituents are independently selected from the group consisting of halo, cyano, nitro, trifluoromethyl, alkoxy and alkyl, the latter two having 1 to 4 carbon atoms, inclusive; or Rl and R2 when combined and taken together with the nitrogen atom to which they are attached form a nitrogen-containing heterocyclic ring;

in an anhydrous medium, at a COS/amine mole ratio of at least about 0.502, at a temperature of at least about 10C, and at a pressure of at least about 0 psig;

(b) reacting the product of step (a) with an organic halide of the formula in which R3 is selected from the group consisting of the following ~ubstituted or unsubstituted groups; alkyl, alkenyl, alkynyl, aryl, aralkyl, cycloalkyl, cycloalkenyl, alkoxy, alkenoxy, alkoxyalkyl, alkylthioalkyl, alkoxyalkenyl, alkylthioalkenyl, and heterocyclic ring groups; wherein the substituents are indepen-dently selected from the group consisting of halo, cyano, nitro, ~rifluoromethyl, alkoxy, and alkyl, the latter two having 1 ~o 4 carbon atoms, inclusive;
and 10 80 ~ 40 X i9 selected from ~he group consisting of chlorine, bromine, and iodine;

in an anhydrous medium at a temperature of at least about 60C and a pressure of at least about 0 psig, to form a mixture containing a thiocarbamic acid ester and a salt of the formula R2--NH2+X ; and (c) recovering the thiocarbamic acid ester from the mixture of step (b).

As used in this specification:

the term "alkyl" refers to a monovalent straight or branched chain saturated aliphatic hydrocarbon group of 1 to 12, preferably 2 to 6, and most preferably 2 to 4 carbon stoms, e.g., methyl, ethyl, propyl, i-propyl, t-butyl, 2-methyl octyl, and the like;

the te~m "alkenyl" refers to a monovalent straight or branched chain aliphatic hydrocarbon group of 2 to 8, preferably 2 to 6, and most preferably 2 to 4 carbon atoms, and containing at least one double bond, e.g., allyl, butenyl, butadienyl, and the l~ke;

the term "alkynyl" refers to a monovalent straight or branched chain aliphatic hydrocarbon group of 3 to 6 carbon atoms, and containing at least one triple bond, e.g., propargyl, ~so-butynyl, and the like;

the term "aryl" refers to a monovalent monocyclic or bicyclic aromatic hydrocarbon group, i.e , phenyL and naphthyl;

the term "aralkyl" refers to an alkyl group as defined above, in which a hydrogen atom is substituted by an aryl group as defi~ed ~bove, e.g., benzyl, phenethyl, naphthylmethyl, and the like;

the term "cycloalkyl" refers to a monovalent cyclical saturated hydrocarbon group ~ 3 to 7 carbon atoms, e.g., cyclobutyl, cyclohexyl and the like;

the term r'cycloalkenyl" refers to a monovalent cyclical hydrocarbon group o~ 5 to 7 carbon atoms, and containing at least one double bond, e.g., cyclohexenyl and the like;

the term "alkoxy" re~ers to a monovalen~ straight or branched chain saturated aliphatic hydrocarbonoæy group of 1 to 8, preferably 2 to 6, and most preferably 2 to 4 carbon atoms, e g., ethoxy~ t-butoxy, and the like;

the term "alkenoxy" refers to a monovalent straight or branched chain aliphatic hydrocarbonoxy group of 2 to 8, preferably 2 to 6, and most preferably 2 to 4 carbon atoms, and containing at least one double bond, e.g , butenoxy, pentenoxy, and the like;

the term "alkoxyalkyl" refers to an alkyl group as defined above, in which a hydrogen atom is substi~uted by a phenoxy or alkoxy group as defined above, e.g., phenoxyethyl, methoxyethyl, ethoxyethyl, and the like;

the term "alkylthioalkyl" refers to an alkyl group as defined above, in which a hydrogen atom is substituted by a monovalent straight or branched chain ~aturated aliphatic hydro-carbonthio group of 1 to 8 carbon atoms, or a phenylthio group, e.g., methylthioethyl, phenylthioethyl, and the like;

the tenm "alkoxyalkenyl" refers to an alkenyl group as defined above, in which a hydrogen atom is substitu~ed by an alkoxy group as def~ned above, e.g., ethoxybutenyl and the like;

the term "alkylthioalkenyl" refer~ to an alkenyl group as defined above, in which a hydrogen atom is substituted by a monovalent straight or branched chain saturated aliphatic hydro-carbonthio group of 1 to 8 carbon atoms, e.g., ethylthiobutenyl, and the like;

the term "halo" refers to chloro, fluoro, and bromo; and the term "he~erocyclic ring group" refers to a monovalent group containing both carbon atoms and non-carbon atoms joined together to form a monocyclic, bicyclic, or ~ricyclic ring of 3 to 8 atoms per cycle. The ring may be saturated or may contain one or more double bonds. The tenm "non-carbon atom" refers to a nitrogen, phosphorus, or sulfur atom. When two or more non-carbon a~oms are present in one group, such atoms may be the same or different. Examples of nitrogen-containing heterocyclic ring groups which Rl and R2 combined a~d taken together with ~he nitrogen atom to which they are attached may represent are pyrryl, pyrrolydyl, pyrazolyl, aziridinyl, oxaæolydyl, thiazolydyl, and polyalkyleneimine having 2 to 6 carbon atoms. Examples of hetero~
cyclic ring groups which Rl and R2 individually and R3 may repre-sent are furyl, thiofuryl, pyranyl, benzofuryl, tetrahytro~uryl, and those named above. The term "heterocyclic ring group" when applied to Rl and R2 individually and R3 is further intended to include methyl groups in which one hydrogen atom is substituted by a monocyclic, bicyclic or tricyclic ring of the above descrip-tion. Examples of the latter a_e furfuryl and tetrahydrofurfuryl.

All carbon atoms ranges stated herein are intended to be inclusive of their stated upper and lower limit8.

Detailed Description of the Invention According to the process of the invention, a mole of carbonyl sulfide is reacted with approximately two moles of 8 primary or secondary amine, preferably a secondary amine, and the product subsequently reacted with an organic halide to produce the desired product.

The COS/amine reaction must be performed under anhydrous - conditions, in order to prevent combination of the COS w~th water, with the re~lting formation of H2S and subsequent imp~rities. For maximum conversion of the amine, an excess of COS is used, such that the COS/amine mole ratio is at least about 0.502, preferably from about 0.502 to about 0.75, and st preferably from about 0.515 to about 0.55. While the pressure and temperature at which this reaction is carried out are not essential to the invention, it will be convenient to operate at a temperature from about 10C
to ab~ut 160C, preferably from about 20C to about 110C, and at ~ 0 8V Z 40 a pressure from about 0 psig to about 500 psig, preferably from about 10 psig to about 150 psig.

The COS/amine reaction can be conducted in the absence of a solvent or in the presence of any anhydrous aprotic s91vent.
The term "aprotic solvent" refers to an organic solvent that does not offer or accept protons. Examples of such solvents are ben-zene, toluene, alkanes, and halides thereof. Solvent~ which are not suitable over a broad temperature range are those that hydrolyze the reaction product, e.g , water, alcohols, aldehydes, or ketones. Preferably, the reaction is run with either no solvent or with the organ~c halide or the product thiocarbamic acid ester as a solvent. Most preferably, either no solvent or the thiocarbamic acid ester is used.

The second reaction step, wherein the amine salt formed in the COS/amine reaction ~s reactet with organic halide, is also performed under anhydrous conditions. This is particularly important siw e at temperatures above about 60~C, the amine salt decomposes and releasesl gaseous COS which, in the presence of water, converts to H2S and C02, The H2S combines with the unreacted salt and the product ester to form by-products and reduce the purity of the desired reaction product.

Another advantage of operati~n in an anhydro~s medium is that the range of organic halides which can be used is broadened to include less reactive organic halides which will react readily only ak temperatures in excess of about 60C.
Examples of the lat~er are the lower al~yl chlorides having 1-4 ~08VZ40 carbon atoms Operation in a non-anhydrous medium at such tempera-tures would involve a large amount of by-product formation, since the rate of liberation of carbonyl sulfide increases with increasing temperature. In anhydrous media, temperature has essentially no effect on by-product formation, since carbonyl sulfide in the absence of water does not form hydrogen sulfide to combine with the salt of the ester.

The amine salt/organic halide reaction is thus performed at a temperature of at least about 60C, preferably from about 60C
to abou~ 160C, and most preferably from about 70C to about 110C.
Furthermore, the reaction is performed at a pressure of at least about 0 psig, preferably from about 0 psig to about 500 psig, most preferably from about 10 psig to about 150 psig.

This reaction can also be conducted either in the absence of a solvent or in the presence of an anhydrous aprotic solvent, as described above for the COS/amine reaction, Preferably, either no solvent is used, or the organic halide or product thiocarbamic acid ester is used. Most preferably, either no solvent or the product thiocarbamic acid ester is used.

For improved conversion of the amine salt to the thio-carbamic acid ester, an excess of the organic halide can be used, such that the mole ratio of the halide to the salt is from about 1.0 to about 1.5, preferably from about 1.03 to about 1.1 E~AMPLES
In Experiments 1 th~ough 7 below9 the appropriate amine was placed in a pressure vessel and the appropriate organic halide ~ 0 8~'~ 4~

was added to the amine. The vessel was then closed and carbonyl sulfide was added by bubblin~ below the liquid surface. The contents were stirred with a magnetic stirrer and placed in a heated bath. Reaction was completed in 1 hour or less. The amine hydrochloride was dissolved in water and removed from the product.
The resulting product was washed with water and dilute aqueous HCl. The aqueous portions were then extracted with hexane and the product was stripped under vacuum.

In Experiment 8, the amine was first satura~ed with carbonyl sulfide at atmospheric pressure. Saturation was then maintained while the organic halide was added.

Table I below lists the reactants used in the experiments and the thiocarbamic acid esters obtained therefrom. Table II
lists the reactant ratios and reaction conditions of each experiment~ with the results obtained in terms o~ yield and purity.

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1~8~ 29UD
Com~ound Activity Data As stated hereinabove, the thiocarbamic acid esters prepared by the process of the invention are useful as pre-emergence and post-emergence herbicides, growth ~nhibitors, and insecticides. Herbic~e activity of some of the compounds made in the above examples by the process of the invention was detenmined by the following screening procedures Pre-Emergence Herbicide Screenin~ Test Using an analytical balance, 20 mg of the compound to be tested is weighed out on a piece of glassine weighing paper.
The paper and compounds are placed in a 30 ml wide-mouth bottle and 3 ml of acetone containing 1% Tween 20~ (an emulsifying agent defined as a polyoxyethylene sorbitan monolaurate) is added to dissolve the compound. If the material is not ~luble in acetone, another solvent such as water, alcohol or dimethylfonmamide (D~F) is used instead. When M~ is used, only 0.5 ml or less is used to dissolve the compound and then another solvent is used to make the volume up to 3 ml. The 3 ml of solution is sprayed uniformly on the soil contained in a small fiber flat one day after planting weed seeds in the flat of soil. A No. 152 DeVilbiss atomizer is used to apply the spray using compressed air at a pressure of 5 psig. The rate of application is 8 lb/acre and the spray vol~me is 143 gal/acre.

On the date preceding treatment, the fiber flat, which is 7 inches long, 5 inches wide and 2.75 inches deep, is filled to a depth of 2 inches with loamy sand soil. Seeds of seven different weed species are planted in ndiv dual rows using one 10 8~ ~ 40 species per row across the width of the flat. The seeds are covered with soil so that they are planted at a depth of 0.5 inch. The seeds used are hairy crabgrass (Di~itaria san~uinalis), yellow foxtail (SPtaria glauca), redroot pigweed (Amaranthus rectrofle~us), Indian mustard (Brassica juncea), curly dock (Rumex crisDus~, watergrass (Echinochloa crus~alli), and red oat (Avena sativa).
Ample seeds are planted to give about 20 to 50 seedlings per row after emergence depending on the size of the plants.

After treatment, the flats are placed in the greenhouse at a temperature of 70 to 85F and watered by sprinkling. Two week~ after treatment the degree of injury or control ~s deter-mined by comparison with untreated check plants of the same age.
The injury rating from 0 to 100% is recorded for each species as percent control with 0% representing no injury and 100%
representing complete kill.

Post-Emergence Herbicide Screenin~ Test Seeds of six plant species, including hairy crabgrass, watergrass, red oat, mustard, curly dock and Pinto beans (Phaseolus vul~aris) are planted in the fiber flats as described above or pre-emergence screening. The flats are placed in the gree~house at 70 to 85F and watered daily with a sprinkler.
About 10 to 14 days after planting when the primary leaves of the bean plants are a~.lost fully expanded and the first trifoliate leaves are just starting to form, the plantæ are sprayed. The spray is prepared by weighing out 20 mg of the test compound, dissolving it in 5 ml of acetone containing 1% Tween 20~ and then - adding 5 ml of water. The solution is sprayed on the foliage 108~)240 using a No. 152 DeVilbiss atomizer at an air pressure of 5 psig.
The spray concentration is 0.2 and the rate is 8 lb/acre. The spray volume is 476 gal/acre. Injury ratings are recorded 14 days after treatment. The rating system is the same as described above in pre-emergence test.

The results of these tests are shown in Table III.

10~V'~ 40 TABLE III
Herbicide Activity Experiment Pre-Emer~ence: Percent Control at 8 lb/acre No. CG FT WG R0 PW MD CD

3 20 90 95 100 0 10 40

4 90 80 97 100 30 20 0 Product of Post-Emer~ence: Percent Control at 8 lb/acre Experiment N~ o. CG WG R0 MD CD PB

. .
Symbols:
CG : Hairy crabgrass mg : milligrams FT : yellow foxtail ml : milliliters r~G : watergrasg p3ig: pounds ~er square - ~nch gau~e R0 : red oat gal : gallons PW : redroot pigweed Lb : pounds MD : Indian mustard CD : curly dock PB : Pinto beans - -19- :

Claims (19)

WHAT IS CLAIMED IS:

1. A process for the preparation of a thiocarbamic acid ester which comprises (a) reacting COS with an amine of the formula in which R1 and R2 are independently selected from the group consisting of hydrogen and the following substitu-ted or unsubstituted groups: alkyl, alkenyl, alkynyl, aryl, aralkyl, cycloalkyl, cycloalkenyl, alkoxy, alkenoxy, alkoxyalkyl, alkylthioalkyl, alkoxyalkenyl, alkylthioalkenyl, and heterocyclic ring groups; wherein the substituents are indepen-dently selected from the group consisting of halo, cyano, nitro, trifluoromethyl, alkoxy and alkyl, the latter two having 1 to 4 carbon atoms, inclusive; or R1 and R2 when combined and taken together with the nitrogen atom to which they are attached form a nitrogen-containing heterocyclic ring;
in an anhydrous medium, at a COS/amine mole ratio of at least about 0.502, at a temperature of at least about 10°C, and at a pressure of at least about 0 psig;
(b) reacting the product of step (a) with an organic halide of the formula in which R3 is selected from the group consisting of the following substituted or unsubstituted groups: alkyl, alkenyl, alkynyl, aryl, aralkyl, cycloalkyl, cycloalkenyl, alkoxy, alkenoxy, alkoxyalkyl, alkylthioalkyl, alkoxyalkenyl, alkylthioalkenyl, and heterocyclic ring groups; wherein the sub-stituents are independently selected from the group consisting of halo, cyano, nitro, trifluoromethyl, alkoxy and alkyl, the latter two having 1 to 4 carbon atoms, inclusive; and X is selected from the group consisting of chlorine, bromine, and iodine;
in an anhydrous medium at a temperature of at least about 60°C
and a pressure of at least about 0 psig, to form a mixture contain-ing a thiocarbamic acid ester and a salt of the formula ; and (c) recovering the thiocarbamic acid ester from the mixture of step (b).

2. The process of Claim 1 in which steps (a) and (b) occur in the absence of a solvent other than the thiocarbamic acid ester produced in step (b) or the organic halide of step (b).

3. The process of Claim 1 in which step (a) is carried out at a temperature of from about 10°C to about 160°C, at a pres-sure of from about 0 psig to about 500 psig, and at a COS/amine mole ratio of from about 0.502 to about 0.75; and step (b) is carried out at a temperature from about 60°C to about 160°C, and at a pressure of from about 0 psig to about 500 psig.

4. The process of Claim 1 in which step (a) is carried out at a temperature of from about 20°C to about 110°C, at a pres-sure of from about 10 psig to about 150 psig, and at a COS/amine mole ratio of from about 0.515 to about 0.55; and step (b) is carried out at a temperature of from about 70°C to about 110°C, and at a pressure of from about 10 psig to about 150 psig.

5. The process of Claim 1 in which the mole ratio in step (b) of the organic halide to the product of step (a) is from about 1.0 to about 1.5.

6. The process of Claim 1 in which the mole ratio in step (b) of the organic halide to the product of step (c) is from about 1.03 to about 1.1.

7. The process of Claim 1 in which steps (a) and (b) are carried out simultaneously.

8. The process of Claim 1 in which R1 and R2 taken together with the nitrogen atom to which they are attached represent polyalkyleneimine having 2 to 6 carbons atoms, and R3 is alkyl having 1 to 12 carbon atoms.

9. The process of Claim 1 in which R1, R2, and R3 are independently alkyl having 1 to 12 carbon atoms.

10. The process of Claim 1 in which R1 and R2 are independently alkyl having 1 to 12 carbon atoms, and R3 is benzyl.

11. The process of Claim 1 in which R1 and R2 are independently alkyl having 1 to 12 carbon atoms, and R3 is haloalkenyl having 2 to 8 carbon atoms.

12. The process of Claim 4 in which R1 and R2 are independently alkyl having from 1 to 12 carbon atoms, and R3 is substituted benzyl in which the substituents are selected from the group consisting of chloro, alkoxy having 1 to 4 carbon atoms, nitro, and trifluoromethyl.

13. The process of Claim 4 in which R1 is n-propyl, R2 is n-propyl, R3 is ethyl, and X is chlorine,

14. The process of Claim 4 in which R1 is isobutyl, R2 is isobutyl, R3 is ethyl, and X is chlorine.

15. The process of Claim 4 in which R1 and R2 taken together with the nitrogen atom to which they are attached are hexamethyleneimine; R3 is ethyl; and X is chorine.

16. The process of Claim 4 in which R1 is n-propyl,, R2 is n-propyl, R3 is n-propyl, and X is chlorine.

17. The process of Claim 4 in which R1 is ethyl, R2 is n-butyl, R3 is n-propyl, and X is chlorine.

18. The process of Claim 4 in which R1 is ethyl, R2 is cyclohexyl, R3 is ethyl, and X is chlorine.

19. The process of Claim 4 in which R1 is ethyl, R2 is ethyl, R3 is p-chlorobenzyl, and X is chlorine.